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Why are hundreds of female workers collapsing at Cambodian factories? And could it have something to do with Pokémon cartoons, "World Trade Center syndrome" and the Tanganyika laughter epidemic of 1962?

Last week a team of experts from the U.N.'s International Labour Organization (ILO) gathered in Phnom Penh to seek an answer to the first question. In the past three months, at least 1,200 workers at seven garment and shoe factories have reported feeling dizzy, nauseated, exhausted or short of breath, and hundreds have been briefly hospitalized. No definitive explanation has yet been given for these so-called mass faintings. One baffled reporter described them as "unique to Cambodia."
(Read how companies are abandoning Chinese factories in search of cheaper options.)

Hardly. It's been almost 50 years since girls at a boarding school in Tanganyika (now Tanzania) were struck by an illness whose symptoms  fainting, nausea and helpless laughter  soon spread to other communities. Or consider the Pokémon contagion in 1997, when 12,000 Japanese children experienced fits, nausea and shortness of breath after watching a television cartoon. Sufferers of World Trade Center syndrome, meanwhile, blamed proximity to Ground Zero for coughs and other respiratory problems long after airborne contaminants posed any health threat.

All these are examples of mass hysteria, a bizarre yet surprisingly common phenomenon that is increasingly recognized as a significant health and social problem. For centuries it has crossed cultures and religions, taking on different forms to keep pace with popular obsessions and fears. In our post-9/11 world, it thrives on the anxiety caused by terrorist attacks, nuclear radiation and environmental gloom. "At any one time there are probably hundreds of episodes happening all around the world," says Simon Wessely, a psychology professor at the Institute of Psychiatry at King's College London. "They just don't normally get reported."

While New York City firefighters and Tokyo schoolchildren have both succumbed to what experts categorize as a mass sociogenic or psychogenic illness, young women are particularly vulnerable  and in Cambodia they make up most of the garment industry's 350,000-strong workforce. Conditions for workers have improved over the years, says the ILO, but few would envy their lot. Women leave their villages to toil in suburban factories for long hours and low pay, often making products for famous Western brands such as Puma and H&M. They live in grim communal shacks, eating sparingly so that they can send as much money as possible back to their homes.(Read about the burden of good intentions in manufacturing.)

"Stress, boredom, concern about their children and other factors among young females could trigger psychogenic fainting or other illnesses," says Ruth Engs, a professor of applied health sciences at Indiana University who investigated an outbreak of mass hysteria at a Midwestern university in 1995 after false reports of a toxic leak caused dozens of people to fall ill. "Poor ventilation, few breaks, stress from piecework production and other workplace conditions would all be contributing factors."